Inter-vehicle communication devices have been widely known which gives support such as vehicle control (auto cruise control, for example) and follow-up driving by sharing vehicle information among a plurality of vehicles using inter-vehicle communication. However, the conventional inter-vehicle communication devices, which repeat transfer of data in such a manner that a transmission source vehicle transmits data to surrounding vehicles, and which receive the data and further transmit the data to their surrounding vehicles, have a problem of incurring congestion due to excessive retransfer of the same data because of the repeated transfer of the data even after the completion of the data sharing. There is another problem in that limiting the number of times of the transfer to solve the problem of the congestion has an adverse effect on the support such as that some vehicles cannot receive the data. In addition, if the congestion occurs, it can bring about communication delay throughout the inter-vehicle communication, thus offering a problem of affecting other support services using the inter-vehicle communication.
Thus, in Patent Document 1 and Patent Document 2, for example, when sharing data among a plurality of vehicles, a transmission source vehicle divides data and transmits the divided data separately to other vehicles, and the vehicles that receive the divided data transmit and receive unreceived divided data from each other, thereby reducing the amount of the transmission data and suppressing the congestion.
In addition, Patent. Document 3, for example, constructs a network at the time of the inter-vehicle communication between a plurality of vehicles, and transfers data in accordance with a communication path in the network, thereby preventing excessive data transfer.